I got hooked on FBreader on the N800 when Tor was promoting their unlaunched website by giving away non-DRM ebooks from their sci-fi and fantasy catalog. I read all of the freebies and after tor.com was launched, the freebies dried up and Tor doesn't (yet?) have an ebook store. So I started buying e-books at fictionwise.com, which has a large catalog with quite a few books in non-DRM formats. The latest bestsellers are DRM'ed, so it's not exactly the same books you can get on a Kindle, but there's a good selection that is compatible with FBreader on the N800.